L7224U Acquastat temp settings

[remodeler]

Hi there:
I recently had a L7224U Aquastat (Honeywell's replacement for L8124)installed on a Weil-Mclean Oil Burner. I have had some difficulty in setting the proper temperature limits. This boiler provides space heat as well as Domestic Hot Water. The boiler manufacturer reccomends the following settings:
High Limit = 200 F
Low Limit = 190 F
High Limit Differential = 15 F
Low Limit Differential = 10 F

With these settings, the circulator control does not seem to operate properly as there is a lot of jitter in the control (burner comes on and off with very small changes in temperatures, every 1-3 seconds).

The tech sheet states that "setting the Low Limit less than the High Differential below the High Limit *is not allowed* as improper circulator and Zone Control functions could result". I beleive the Boiler Manufacturer's reccomendation cause this state to exist.

Has anyone had experience with this particular controller. It does not seem that the old L8124 settings trasfer directly.

I don't think there is anything wrong with the controller, or the temp probe, its just a matter of setting the correct limits.

Thank-you.

[beenthere]

You misunderstnding the sheet.

Set it to the same settings the old control had.

If you don't remmember them, start with 160 low, and 200 hi, and let the dif's where they are.

[remodeler]

I just re-read my post and found a typo-

the boiler manufacture reccomends a high setting of 210F, not 200F as I previously wrote.

With a high setting of 210F, I think I am operating in an an unacceptable region.

Old setting were unclear since the acquastat was not functioning correctly.

I will try the suggestion of lowering the low limit and see how that works out. Presumably this will reduce burner cycling.


Thanks.

[casturbo]

Originally posted by remodeler
I just re-read my post and found a typo-

the boiler manufacture reccomends a high setting of 210F, not 200F as I previously wrote.

With a high setting of 210F, I think I am operating in an an unacceptable region.

Running the boiler aquastat limit at 210° is going to blow the relief valve, guaranteed, especially on that McLain high efficiency oil boiler. The issue comes up since the boiler continues to gain temperature AFTER the burner shut-off since the cast iron sections are still extremely hot after the boiler reaches 210°. Even with the boiler underpressure it will boil. And if the boiler for some reason has no pressure on it, it will blow steam out the relief. So why do some boiler manufacturers recommend you COULD set the high limit that high?....because it's their way to get alot of BTU out of a small boiler. Real bad way to rate a boiler, but alot do it....too bad it don't work in the real world. That being said, set the low limit at 160°, high limit on 180° or maybe 190° since you got the more accurate thermistor aquastat now, and set the differentials tight if the domestic hot water does NOT have a tempering valve, differentials far apart if there is a tempering valve. Better yet, install a holding tank for the hot water and drop all settings at least 20° and enjoy the oil savings.

[beenthere]

Ther better be a tempering valve on a boiler with tankless coil, its part of the code.

As stated don't set the high limit to 210, it can cause alot of trouble. Unless your baseboard isn't enough to heat your house at 200°.

With the low set to 160, set the diff to 10, if it cycles too much, then try 15, then 20, if need be.

[remodeler]

There is a tempering valve on the unit.

I've notice the overheating heating issue with setting the high limit to 210F- the temp continues to rise after the burner shuts off. It can reach as high as 220F, which is clearly a problem.

Thanks for the advice, I'll try the lower settings.

I'm still unclear on a technical point which seems to be particular to the L7224U: Can the low limit be lower than the high limit minus the high limit differential?

Example:
High limit = 190F
High limit diff = 20F
Low limit = 160 F
Low Limit diff = 10F

If I understand the tech sheet correctly, I cannot have these settings. I either need to change the high limit differential to 30F or more. Or I need to increase the low limit to 170F or more.

Is this a correct understanding of the contraint imposed on this particular acquastat?

Thanks again for your input.

[beenthere]

No, you can set the low limit lower.

If it couldn't be set lower, then the circ might stop running but the burner not come backon till the boiler lost more heat.

The burner should come on before the low limit shuts the heat circ off.

So,

hi limit 190
diff 20
lo limt 160
diff 10
is ok.